any one sloved today's puzzle which graded level hard? and would like to share your methods to complete those squares?
I started playing sudoku puzzle last week but I have never solved hard level or upper level's puzzle.
I read some books but it's helpless to solve higher level puzzles with only knowledge of those three common skills

Just do as much as you can and then share with us as where you got stuck at. Then we can help you to get to the next step and go from there. Everybody takes different routes on getting to a certain point so it can get confusing just explaining how one person arrived at certain point of the puzzle.

any one sloved today's puzzle which graded level hard? and would like to share your methods to complete those squares?
I started playing sudoku puzzle last week but I have never solved hard level or upper level's puzzle.
I read some books but it's helpless to solve higher level puzzles with only knowledge of those three common skills

I did this puzzle with the following steps:

1. Put in the easy numbers. If you look at it there are 9's in all but two 3x3 boxes.
2. Look for the 3x3 boxes, rows or columns that have the most numbers in them, put all the possible numbers (write small with a pencil) in them. As you are doing this make a note of any numbers within a 3x3 box that c are in a straight line. That is, within a 3x3 box if you are figuring out where the 2's are and you find that there are only two or three possible places for the 2's and they happen to be in a straight line (in one row or column). I would put a pencil circle around these because they can only be in that part of the row or column and cannot be in another 3x3 box in that same row or column. Move around the puzzle until all the boxes have all the possibilities in them. As you do this, you will get some of them figured out and you will need to erase those from the adjacent boxes.
4. Start going through each column, row and box and look for couplets. These are sets of 2 numbers that are together only in two boxes. That means no other numbers can be in there and you can erase the other numbers. This also works for sets of 3 numbers that are together only in 3 boxes. I have yet to see a quadruple, but I've only been doing this for short time.
5. Keep cycling through each row, column and box. If you get stuck after this, post what you have on this board (include all the possible numbers you have) and someone will help you, explaining your next step. (I did this last week).